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 $65.52   6.297%   $69.6458   $69.65   $69.65   $69.60  
  Purchase #2 $225.58   8.860%   $245.5664   $245.57   $245.55   $245.60  
  Purchase #3 $198.51   11.289%   $220.9198   $220.92   $220.90   $220.90  
  Purchase #4 $207.85   11.763%   $232.2994   $232.30   $232.30   $232.30  
  Purchase #5 $191.57   4.132%   $199.4857   $199.49   $199.50   $199.50  
  Purchase #6 $111.61   3.332%   $115.3288   $115.33   $115.35   $115.30  
  Purchase #7 $133.33   12.794%   $150.3882   $150.39   $150.40   $150.40  
  7 purchase totals = $1,133.97       $1,233.6341   $1,233.65   $1,233.65   $1,233.60