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 $174.65   12.136%   $195.8455   $195.85   $195.85   $195.80  
  Purchase #2 $215.39   9.732%   $236.3518   $236.35   $236.35   $236.40  
  Purchase #3 $171.59   6.471%   $182.6936   $182.69   $182.70   $182.70  
  Purchase #4 $232.99   9.264%   $254.5742   $254.57   $254.55   $254.60  
  Purchase #5 $45.82   7.497%   $49.2551   $49.26   $49.25   $49.30  
  Purchase #6 $134.98   12.403%   $151.7216   $151.72   $151.70   $151.70  
  Purchase #7 $223.59   7.434%   $240.2117   $240.21   $240.20   $240.20  
  7 purchase totals = $1,199.01       $1,310.6535   $1,310.65   $1,310.60   $1,310.70