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 $87.56   5.177%   $92.093   $92.09   $92.10   $92.10  
  Purchase #2 $209.60   10.144%   $230.8618   $230.86   $230.85   $230.90  
  Purchase #3 $55.98   4.191%   $58.3261   $58.33   $58.35   $58.30  
  Purchase #4 $144.61   6.446%   $153.9316   $153.93   $153.95   $153.90  
  Purchase #5 $60.97   4.184%   $63.521   $63.52   $63.50   $63.50  
  Purchase #6 $138.80   6.115%   $147.2876   $147.29   $147.30   $147.30  
  Purchase #7 $56.25   4.657%   $58.8696   $58.87   $58.85   $58.90  
  7 purchase totals = $753.77       $804.8907   $804.89   $804.90   $804.90