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 $113.41   11.561%   $126.5213   $126.52   $126.50   $126.50  
  Purchase #2 $98.30   12.636%   $110.7212   $110.72   $110.70   $110.70  
  Purchase #3 $220.74   11.756%   $246.6902   $246.69   $246.70   $246.70  
  Purchase #4 $68.44   8.631%   $74.3471   $74.35   $74.35   $74.30  
  Purchase #5 $187.97   11.212%   $209.0452   $209.05   $209.05   $209.00  
  Purchase #6 $83.86   8.735%   $91.1852   $91.19   $91.20   $91.20  
  Purchase #7 $184.45   5.215%   $194.0691   $194.07   $194.05   $194.10  
  7 purchase totals = $957.17       $1,052.5793   $1,052.59   $1,052.55   $1,052.50