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 $59.56   4.616%   $62.3093   $62.31   $62.30   $62.30  
  Purchase #2 $149.27   4.539%   $156.0454   $156.05   $156.05   $156.00  
  Purchase #3 $103.76   12.586%   $116.8192   $116.82   $116.80   $116.80  
  Purchase #4 $118.84   13.629%   $135.0367   $135.04   $135.05   $135.00  
  Purchase #5 $79.44   8.185%   $85.9422   $85.94   $85.95   $85.90  
  Purchase #6 $200.34   7.597%   $215.5598   $215.56   $215.55   $215.60  
  Purchase #7 $177.39   6.570%   $189.0445   $189.04   $189.05   $189.00  
  7 purchase totals = $888.60       $960.7571   $960.76   $960.75   $960.60