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 $46.59   8.440%   $50.5222   $50.52   $50.50   $50.50  
  Purchase #2 $45.93   13.813%   $52.2743   $52.27   $52.25   $52.30  
  Purchase #3 $225.45   11.198%   $250.6959   $250.70   $250.70   $250.70  
  Purchase #4 $246.45   10.373%   $272.0143   $272.01   $272.00   $272.00  
  Purchase #5 $44.47   3.479%   $46.0171   $46.02   $46.00   $46.00  
  Purchase #6 $114.64   6.171%   $121.7144   $121.71   $121.70   $121.70  
  Purchase #7 $164.86   10.321%   $181.8752   $181.88   $181.90   $181.90  
  7 purchase totals = $888.39       $975.1134   $975.11   $975.05   $975.10