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 $126.43   5.206%   $133.0119   $133.01   $133.00   $133.00  
  Purchase #2 $5.41   6.670%   $5.7708   $5.77   $5.75   $5.80  
  Purchase #3 $17.65   5.832%   $18.6793   $18.68   $18.70   $18.70  
  Purchase #4 $58.87   3.833%   $61.1265   $61.13   $61.15   $61.10  
  Purchase #5 $159.96   10.823%   $177.2725   $177.27   $177.25   $177.30  
  Purchase #6 $180.52   11.499%   $201.278   $201.28   $201.30   $201.30  
  Purchase #7 $100.95   9.677%   $110.7189   $110.72   $110.70   $110.70  
  7 purchase totals = $649.79       $707.8579   $707.86   $707.85   $707.90