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 $242.42   11.359%   $269.9565   $269.96   $269.95   $270.00  
  Purchase #2 $82.90   11.654%   $92.5612   $92.56   $92.55   $92.60  
  Purchase #3 $145.61   5.290%   $153.3128   $153.31   $153.30   $153.30  
  Purchase #4 $243.57   9.655%   $267.0867   $267.09   $267.10   $267.10  
  Purchase #5 $45.40   8.661%   $49.3321   $49.33   $49.35   $49.30  
  Purchase #6 $72.41   13.401%   $82.1137   $82.11   $82.10   $82.10  
  Purchase #7 $121.93   9.684%   $133.7377   $133.74   $133.75   $133.70  
  7 purchase totals = $954.24       $1,048.1007   $1,048.10   $1,048.10   $1,048.10