Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $205.87   5.270%   $216.7193   $216.72   $216.70   $216.70  
  Purchase #2 $209.39   4.391%   $218.5843   $218.58   $218.60   $218.60  
  Purchase #3 $123.58   9.252%   $135.0136   $135.01   $135.00   $135.00  
  Purchase #4 $195.43   5.227%   $205.6451   $205.65   $205.65   $205.60  
  Purchase #5 $115.50   11.434%   $128.7063   $128.71   $128.70   $128.70  
  Purchase #6 $218.73   11.214%   $243.2584   $243.26   $243.25   $243.30  
  Purchase #7 $202.37   3.869%   $210.1997   $210.20   $210.20   $210.20  
  7 purchase totals = $1,270.87       $1,358.1267   $1,358.13   $1,358.10   $1,358.10