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 $227.51   8.840%   $247.6219   $247.62   $247.60   $247.60  
  Purchase #2 $172.78   11.825%   $193.2112   $193.21   $193.20   $193.20  
  Purchase #3 $115.88   8.109%   $125.2767   $125.28   $125.30   $125.30  
  Purchase #4 $152.28   5.168%   $160.1498   $160.15   $160.15   $160.10  
  Purchase #5 $81.80   7.258%   $87.737   $87.74   $87.75   $87.70  
  Purchase #6 $16.58   11.612%   $18.5053   $18.51   $18.50   $18.50  
  Purchase #7 $250.46   5.415%   $264.0224   $264.02   $264.00   $264.00  
  7 purchase totals = $1,017.29       $1,096.5243   $1,096.53   $1,096.50   $1,096.40