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 $172.37   12.614%   $194.1128   $194.11   $194.10   $194.10  
  Purchase #2 $133.41   12.171%   $149.6473   $149.65   $149.65   $149.60  
  Purchase #3 $62.77   12.263%   $70.4675   $70.47   $70.45   $70.50  
  Purchase #4 $234.90   11.782%   $262.5759   $262.58   $262.60   $262.60  
  Purchase #5 $126.69   4.135%   $131.9286   $131.93   $131.95   $131.90  
  Purchase #6 $132.66   12.614%   $149.3937   $149.39   $149.40   $149.40  
  Purchase #7 $220.48   7.689%   $237.4327   $237.43   $237.45   $237.40  
  7 purchase totals = $1,083.28       $1,195.5585   $1,195.56   $1,195.60   $1,195.50