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 $181.86   8.758%   $197.7873   $197.79   $197.80   $197.80  
  Purchase #2 $105.93   13.107%   $119.8142   $119.81   $119.80   $119.80  
  Purchase #3 $66.84   10.860%   $74.0988   $74.10   $74.10   $74.10  
  Purchase #4 $190.58   10.143%   $209.9105   $209.91   $209.90   $209.90  
  Purchase #5 $150.68   11.433%   $167.9072   $167.91   $167.90   $167.90  
  Purchase #6 $109.94   8.471%   $119.253   $119.25   $119.25   $119.30  
  Purchase #7 $148.43   7.573%   $159.6706   $159.67   $159.65   $159.70  
  7 purchase totals = $954.26       $1,048.4416   $1,048.44   $1,048.40   $1,048.50