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 $231.76   6.507%   $246.8406   $246.84   $246.85   $246.80  
  Purchase #2 $12.44   3.621%   $12.8905   $12.89   $12.90   $12.90  
  Purchase #3 $61.80   5.644%   $65.288   $65.29   $65.30   $65.30  
  Purchase #4 $244.61   12.733%   $275.7562   $275.76   $275.75   $275.80  
  Purchase #5 $206.61   6.321%   $219.6698   $219.67   $219.65   $219.70  
  Purchase #6 $238.94   9.114%   $260.717   $260.72   $260.70   $260.70  
  Purchase #7 $15.70   4.126%   $16.3478   $16.35   $16.35   $16.30  
  7 purchase totals = $1,011.86       $1,097.5099   $1,097.52   $1,097.50   $1,097.50