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 $208.74   4.650%   $218.4464   $218.45   $218.45   $218.40  
  Purchase #2 $210.35   8.417%   $228.0552   $228.06   $228.05   $228.10  
  Purchase #3 $132.29   13.526%   $150.1835   $150.18   $150.20   $150.20  
  Purchase #4 $29.35   7.790%   $31.6364   $31.64   $31.65   $31.60  
  Purchase #5 $229.43   12.695%   $258.5561   $258.56   $258.55   $258.60  
  Purchase #6 $106.43   3.436%   $110.0869   $110.09   $110.10   $110.10  
  Purchase #7 $113.35   8.489%   $122.9723   $122.97   $122.95   $123.00  
  7 purchase totals = $1,029.94       $1,119.9368   $1,119.95   $1,119.95   $1,120.00