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 $210.49   12.208%   $236.1866   $236.19   $236.20   $236.20  
  Purchase #2 $136.85   8.847%   $148.9571   $148.96   $148.95   $149.00  
  Purchase #3 $73.33   10.240%   $80.839   $80.84   $80.85   $80.80  
  Purchase #4 $52.49   13.678%   $59.6696   $59.67   $59.65   $59.70  
  Purchase #5 $234.79   13.217%   $265.8222   $265.82   $265.80   $265.80  
  Purchase #6 $134.73   6.288%   $143.2018   $143.20   $143.20   $143.20  
  Purchase #7 $160.72   12.588%   $180.9514   $180.95   $180.95   $181.00  
  7 purchase totals = $1,003.40       $1,115.6277   $1,115.63   $1,115.60   $1,115.70