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 $169.65   8.447%   $183.9803   $183.98   $184.00   $184.00  
  Purchase #2 $132.30   6.366%   $140.7222   $140.72   $140.70   $140.70  
  Purchase #3 $139.96   5.271%   $147.3373   $147.34   $147.35   $147.30  
  Purchase #4 $134.65   6.809%   $143.8183   $143.82   $143.80   $143.80  
  Purchase #5 $54.85   10.734%   $60.7376   $60.74   $60.75   $60.70  
  Purchase #6 $139.53   4.566%   $145.9009   $145.90   $145.90   $145.90  
  Purchase #7 $125.32   6.165%   $133.046   $133.05   $133.05   $133.00  
  7 purchase totals = $896.26       $955.5426   $955.55   $955.55   $955.40