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 $229.83   10.743%   $254.5206   $254.52   $254.50   $254.50  
  Purchase #2 $113.93   12.123%   $127.7417   $127.74   $127.75   $127.70  
  Purchase #3 $152.55   7.148%   $163.4543   $163.45   $163.45   $163.50  
  Purchase #4 $190.65   6.434%   $202.9164   $202.92   $202.90   $202.90  
  Purchase #5 $55.85   5.436%   $58.886   $58.89   $58.90   $58.90  
  Purchase #6 $96.63   12.387%   $108.5996   $108.60   $108.60   $108.60  
  Purchase #7 $31.75   9.279%   $34.6961   $34.70   $34.70   $34.70  
  7 purchase totals = $871.19       $950.8147   $950.82   $950.80   $950.80