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 $204.89   3.140%   $211.3235   $211.32   $211.30   $211.30  
  Purchase #2 $53.75   9.109%   $58.6461   $58.65   $58.65   $58.60  
  Purchase #3 $142.81   11.722%   $159.5502   $159.55   $159.55   $159.60  
  Purchase #4 $129.56   4.644%   $135.5768   $135.58   $135.60   $135.60  
  Purchase #5 $54.25   3.633%   $56.2209   $56.22   $56.20   $56.20  
  Purchase #6 $143.50   11.771%   $160.3914   $160.39   $160.40   $160.40  
  Purchase #7 $236.77   3.606%   $245.3079   $245.31   $245.30   $245.30  
  7 purchase totals = $965.53       $1,027.0168   $1,027.02   $1,027.00   $1,027.00