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 $186.82   11.115%   $207.585   $207.59   $207.60   $207.60  
  Purchase #2 $135.58   11.869%   $151.672   $151.67   $151.65   $151.70  
  Purchase #3 $119.48   11.319%   $133.0039   $133.00   $133.00   $133.00  
  Purchase #4 $214.79   6.699%   $229.1788   $229.18   $229.20   $229.20  
  Purchase #5 $167.48   7.648%   $180.2889   $180.29   $180.30   $180.30  
  Purchase #6 $171.93   7.201%   $184.3107   $184.31   $184.30   $184.30  
  Purchase #7 $34.50   7.276%   $37.0102   $37.01   $37.00   $37.00  
  7 purchase totals = $1,030.58       $1,123.0495   $1,123.05   $1,123.05   $1,123.10