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 $181.68   12.289%   $204.0067   $204.01   $204.00   $204.00  
  Purchase #2 $172.33   6.692%   $183.8623   $183.86   $183.85   $183.90  
  Purchase #3 $33.79   4.646%   $35.3599   $35.36   $35.35   $35.40  
  Purchase #4 $12.95   3.519%   $13.4057   $13.41   $13.40   $13.40  
  Purchase #5 $98.88   6.188%   $104.9987   $105.00   $105.00   $105.00  
  Purchase #6 $240.28   11.668%   $268.3159   $268.32   $268.30   $268.30  
  Purchase #7 $191.93   6.809%   $204.9985   $205.00   $205.00   $205.00  
  7 purchase totals = $931.84       $1,014.9477   $1,014.96   $1,014.90   $1,015.00