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 $49.29   7.294%   $52.8852   $52.89   $52.90   $52.90  
  Purchase #2 $90.56   4.179%   $94.3445   $94.34   $94.35   $94.30  
  Purchase #3 $180.55   6.173%   $191.6954   $191.70   $191.70   $191.70  
  Purchase #4 $128.42   5.519%   $135.5075   $135.51   $135.50   $135.50  
  Purchase #5 $45.66   12.352%   $51.2999   $51.30   $51.30   $51.30  
  Purchase #6 $232.27   8.802%   $252.7144   $252.71   $252.70   $252.70  
  Purchase #7 $155.77   9.592%   $170.7115   $170.71   $170.70   $170.70  
  7 purchase totals = $882.52       $949.1584   $949.16   $949.15   $949.10