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 $219.68   7.737%   $236.6766   $236.68   $236.70   $236.70  
  Purchase #2 $236.67   13.302%   $268.1518   $268.15   $268.15   $268.20  
  Purchase #3 $167.97   7.753%   $180.9927   $180.99   $181.00   $181.00  
  Purchase #4 $136.44   13.364%   $154.6738   $154.67   $154.65   $154.70  
  Purchase #5 $53.52   5.768%   $56.607   $56.61   $56.60   $56.60  
  Purchase #6 $92.86   3.802%   $96.3905   $96.39   $96.40   $96.40  
  Purchase #7 $245.80   4.488%   $256.8315   $256.83   $256.85   $256.80  
  7 purchase totals = $1,152.94       $1,250.3239   $1,250.32   $1,250.35   $1,250.40