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 $63.72   5.414%   $67.1698   $67.17   $67.15   $67.20  
  Purchase #2 $96.96   9.510%   $106.1809   $106.18   $106.20   $106.20  
  Purchase #3 $120.65   6.293%   $128.2425   $128.24   $128.25   $128.20  
  Purchase #4 $119.69   12.655%   $134.8368   $134.84   $134.85   $134.80  
  Purchase #5 $104.35   3.740%   $108.2527   $108.25   $108.25   $108.30  
  Purchase #6 $148.58   12.837%   $167.6532   $167.65   $167.65   $167.70  
  Purchase #7 $39.93   3.421%   $41.296   $41.30   $41.30   $41.30  
  7 purchase totals = $693.88       $753.6319   $753.63   $753.65   $753.70