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 $87.48   12.731%   $98.6171   $98.62   $98.60   $98.60  
  Purchase #2 $55.64   5.421%   $58.6562   $58.66   $58.65   $58.70  
  Purchase #3 $160.44   13.290%   $181.7625   $181.76   $181.75   $181.80  
  Purchase #4 $207.74   9.657%   $227.8015   $227.80   $227.80   $227.80  
  Purchase #5 $83.53   11.849%   $93.4275   $93.43   $93.45   $93.40  
  Purchase #6 $181.52   5.369%   $191.2658   $191.27   $191.25   $191.30  
  Purchase #7 $193.74   4.120%   $201.7221   $201.72   $201.70   $201.70  
  7 purchase totals = $970.09       $1,053.2527   $1,053.26   $1,053.20   $1,053.30