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 $218.46   12.505%   $245.7784   $245.78   $245.80   $245.80  
  Purchase #2 $104.69   5.277%   $110.2145   $110.21   $110.20   $110.20  
  Purchase #3 $143.74   8.283%   $155.646   $155.65   $155.65   $155.60  
  Purchase #4 $197.70   3.173%   $203.973   $203.97   $203.95   $204.00  
  Purchase #5 $82.78   5.647%   $87.4546   $87.45   $87.45   $87.50  
  Purchase #6 $144.95   9.449%   $158.6463   $158.65   $158.65   $158.60  
  Purchase #7 $58.39   11.251%   $64.9595   $64.96   $64.95   $65.00  
  7 purchase totals = $950.71       $1,026.6723   $1,026.67   $1,026.65   $1,026.70