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 $64.29   11.179%   $71.477   $71.48   $71.50   $71.50  
  Purchase #2 $161.60   11.538%   $180.2454   $180.25   $180.25   $180.20  
  Purchase #3 $62.36   6.357%   $66.3242   $66.32   $66.30   $66.30  
  Purchase #4 $201.68   4.534%   $210.8242   $210.82   $210.80   $210.80  
  Purchase #5 $212.43   7.652%   $228.6851   $228.69   $228.70   $228.70  
  Purchase #6 $56.52   11.451%   $62.9921   $62.99   $63.00   $63.00  
  Purchase #7 $115.81   4.683%   $121.2334   $121.23   $121.25   $121.20  
  7 purchase totals = $874.69       $941.7814   $941.78   $941.80   $941.70