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 $37.98   12.381%   $42.6823   $42.68   $42.70   $42.70  
  Purchase #2 $238.75   12.438%   $268.4457   $268.45   $268.45   $268.40  
  Purchase #3 $162.99   8.260%   $176.453   $176.45   $176.45   $176.50  
  Purchase #4 $216.89   9.303%   $237.0673   $237.07   $237.05   $237.10  
  Purchase #5 $80.80   9.356%   $88.3596   $88.36   $88.35   $88.40  
  Purchase #6 $191.27   13.317%   $216.7414   $216.74   $216.75   $216.70  
  Purchase #7 $108.77   12.269%   $122.115   $122.12   $122.10   $122.10  
  7 purchase totals = $1,037.45       $1,151.8643   $1,151.87   $1,151.85   $1,151.90