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 $128.62   5.756%   $136.0234   $136.02   $136.00   $136.00  
  Purchase #2 $144.71   13.618%   $164.4166   $164.42   $164.40   $164.40  
  Purchase #3 $148.69   12.296%   $166.9729   $166.97   $166.95   $167.00  
  Purchase #4 $225.62   12.834%   $254.5761   $254.58   $254.60   $254.60  
  Purchase #5 $60.96   6.288%   $64.7932   $64.79   $64.80   $64.80  
  Purchase #6 $76.33   11.841%   $85.3682   $85.37   $85.35   $85.40  
  Purchase #7 $175.59   3.282%   $181.3529   $181.35   $181.35   $181.40  
  7 purchase totals = $960.52       $1,053.5033   $1,053.50   $1,053.45   $1,053.60