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 $48.57   8.310%   $52.6062   $52.61   $52.60   $52.60  
  Purchase #2 $10.92   10.305%   $12.0453   $12.05   $12.05   $12.00  
  Purchase #3 $91.87   11.539%   $102.4709   $102.47   $102.45   $102.50  
  Purchase #4 $241.44   10.734%   $267.3562   $267.36   $267.35   $267.40  
  Purchase #5 $102.51   9.242%   $111.984   $111.98   $112.00   $112.00  
  Purchase #6 $110.62   8.406%   $119.9187   $119.92   $119.90   $119.90  
  Purchase #7 $153.36   4.412%   $160.1262   $160.13   $160.15   $160.10  
  7 purchase totals = $759.29       $826.5075   $826.52   $826.50   $826.50