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 $131.64   11.368%   $146.6048   $146.60   $146.60   $146.60  
  Purchase #2 $160.75   8.322%   $174.1276   $174.13   $174.15   $174.10  
  Purchase #3 $171.71   5.463%   $181.0905   $181.09   $181.10   $181.10  
  Purchase #4 $183.51   13.148%   $207.6379   $207.64   $207.65   $207.60  
  Purchase #5 $5.79   11.236%   $6.4406   $6.44   $6.45   $6.40  
  Purchase #6 $73.95   8.334%   $80.113   $80.11   $80.10   $80.10  
  Purchase #7 $11.79   9.534%   $12.9141   $12.91   $12.90   $12.90  
  7 purchase totals = $739.14       $808.9285   $808.92   $808.95   $808.80