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 $142.79   6.620%   $152.2427   $152.24   $152.25   $152.20  
  Purchase #2 $170.69   9.684%   $187.2196   $187.22   $187.20   $187.20  
  Purchase #3 $58.90   11.606%   $65.7359   $65.74   $65.75   $65.70  
  Purchase #4 $76.37   9.705%   $83.7817   $83.78   $83.80   $83.80  
  Purchase #5 $246.80   13.560%   $280.2661   $280.27   $280.25   $280.30  
  Purchase #6 $146.25   9.310%   $159.8659   $159.87   $159.85   $159.90  
  Purchase #7 $98.65   7.689%   $106.2352   $106.24   $106.25   $106.20  
  7 purchase totals = $940.45       $1,035.3471   $1,035.36   $1,035.35   $1,035.30