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 $76.97   8.104%   $83.2076   $83.21   $83.20   $83.20  
  Purchase #2 $218.53   8.200%   $236.4495   $236.45   $236.45   $236.40  
  Purchase #3 $35.48   11.400%   $39.5247   $39.52   $39.50   $39.50  
  Purchase #4 $181.31   4.647%   $189.7355   $189.74   $189.75   $189.70  
  Purchase #5 $196.91   10.551%   $217.686   $217.69   $217.70   $217.70  
  Purchase #6 $219.91   3.844%   $228.3633   $228.36   $228.35   $228.40  
  Purchase #7 $154.33   4.279%   $160.9338   $160.93   $160.95   $160.90  
  7 purchase totals = $1,083.44       $1,155.9004   $1,155.90   $1,155.90   $1,155.80