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 $84.71   3.415%   $87.6028   $87.60   $87.60   $87.60  
  Purchase #2 $110.26   4.144%   $114.8292   $114.83   $114.85   $114.80  
  Purchase #3 $132.98   4.266%   $138.6529   $138.65   $138.65   $138.70  
  Purchase #4 $211.71   4.800%   $221.8721   $221.87   $221.85   $221.90  
  Purchase #5 $60.31   8.128%   $65.212   $65.21   $65.20   $65.20  
  Purchase #6 $169.27   3.697%   $175.5279   $175.53   $175.55   $175.50  
  Purchase #7 $111.74   8.822%   $121.5977   $121.60   $121.60   $121.60  
  7 purchase totals = $880.98       $925.2946   $925.29   $925.30   $925.30