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 $66.59   12.634%   $75.003   $75.00   $75.00   $75.00  
  Purchase #2 $52.33   10.198%   $57.6666   $57.67   $57.65   $57.70  
  Purchase #3 $186.67   9.107%   $203.67   $203.67   $203.65   $203.70  
  Purchase #4 $5.86   3.196%   $6.0473   $6.05   $6.05   $6.00  
  Purchase #5 $45.57   10.142%   $50.1917   $50.19   $50.20   $50.20  
  Purchase #6 $206.29   13.159%   $233.4357   $233.44   $233.45   $233.40  
  Purchase #7 $94.54   12.443%   $106.3036   $106.30   $106.30   $106.30  
  7 purchase totals = $657.85       $732.3179   $732.32   $732.30   $732.30