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 $50.43   12.356%   $56.6611   $56.66   $56.65   $56.70  
  Purchase #2 $184.68   13.644%   $209.8777   $209.88   $209.90   $209.90  
  Purchase #3 $94.83   5.494%   $100.04   $100.04   $100.05   $100.00  
  Purchase #4 $22.51   12.337%   $25.2871   $25.29   $25.30   $25.30  
  Purchase #5 $185.79   9.759%   $203.9212   $203.92   $203.90   $203.90  
  Purchase #6 $174.60   11.731%   $195.0823   $195.08   $195.10   $195.10  
  Purchase #7 $226.92   13.558%   $257.6858   $257.69   $257.70   $257.70  
  7 purchase totals = $939.76       $1,048.5552   $1,048.56   $1,048.60   $1,048.60