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 $168.75   13.404%   $191.3693   $191.37   $191.35   $191.40  
  Purchase #2 $216.55   11.457%   $241.3601   $241.36   $241.35   $241.40  
  Purchase #3 $36.90   6.328%   $39.235   $39.24   $39.25   $39.20  
  Purchase #4 $80.37   9.516%   $88.018   $88.02   $88.00   $88.00  
  Purchase #5 $179.66   11.551%   $200.4125   $200.41   $200.40   $200.40  
  Purchase #6 $169.50   3.669%   $175.719   $175.72   $175.70   $175.70  
  Purchase #7 $80.31   9.176%   $87.6792   $87.68   $87.70   $87.70  
  7 purchase totals = $932.04       $1,023.7931   $1,023.80   $1,023.75   $1,023.80