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 $88.65   6.178%   $94.1268   $94.13   $94.15   $94.10  
  Purchase #2 $204.77   3.644%   $212.2318   $212.23   $212.25   $212.20  
  Purchase #3 $107.43   13.862%   $122.3219   $122.32   $122.30   $122.30  
  Purchase #4 $185.69   8.485%   $201.4458   $201.45   $201.45   $201.40  
  Purchase #5 $27.63   3.592%   $28.6225   $28.62   $28.60   $28.60  
  Purchase #6 $131.60   8.426%   $142.6886   $142.69   $142.70   $142.70  
  Purchase #7 $209.68   10.812%   $232.3506   $232.35   $232.35   $232.40  
  7 purchase totals = $955.45       $1,033.7880   $1,033.79   $1,033.80   $1,033.70