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 $76.74   13.642%   $87.2089   $87.21   $87.20   $87.20  
  Purchase #2 $142.25   10.859%   $157.6969   $157.70   $157.70   $157.70  
  Purchase #3 $228.60   5.394%   $240.9307   $240.93   $240.95   $240.90  
  Purchase #4 $145.67   5.242%   $153.306   $153.31   $153.30   $153.30  
  Purchase #5 $109.38   6.206%   $116.1681   $116.17   $116.15   $116.20  
  Purchase #6 $101.67   8.861%   $110.679   $110.68   $110.70   $110.70  
  Purchase #7 $150.61   10.727%   $166.7659   $166.77   $166.75   $166.80  
  7 purchase totals = $954.92       $1,032.7555   $1,032.77   $1,032.75   $1,032.80