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 $247.32   11.237%   $275.1113   $275.11   $275.10   $275.10  
  Purchase #2 $90.96   3.273%   $93.9371   $93.94   $93.95   $93.90  
  Purchase #3 $103.25   13.179%   $116.8573   $116.86   $116.85   $116.90  
  Purchase #4 $153.44   4.799%   $160.8036   $160.80   $160.80   $160.80  
  Purchase #5 $74.25   4.387%   $77.5073   $77.51   $77.50   $77.50  
  Purchase #6 $218.44   8.558%   $237.1341   $237.13   $237.15   $237.10  
  Purchase #7 $50.74   4.248%   $52.8954   $52.90   $52.90   $52.90  
  7 purchase totals = $938.40       $1,014.2461   $1,014.25   $1,014.25   $1,014.20