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 $65.73   5.415%   $69.2893   $69.29   $69.30   $69.30  
  Purchase #2 $225.67   6.103%   $239.4426   $239.44   $239.45   $239.40  
  Purchase #3 $92.34   5.388%   $97.3153   $97.32   $97.30   $97.30  
  Purchase #4 $130.36   5.821%   $137.9483   $137.95   $137.95   $137.90  
  Purchase #5 $232.78   6.201%   $247.2147   $247.21   $247.20   $247.20  
  Purchase #6 $192.75   12.109%   $216.0901   $216.09   $216.10   $216.10  
  Purchase #7 $150.48   6.516%   $160.2853   $160.29   $160.30   $160.30  
  7 purchase totals = $1,090.11       $1,167.5856   $1,167.59   $1,167.60   $1,167.50