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 $67.83   7.341%   $72.8094   $72.81   $72.80   $72.80  
  Purchase #2 $236.31   6.495%   $251.6583   $251.66   $251.65   $251.70  
  Purchase #3 $74.42   8.309%   $80.6036   $80.60   $80.60   $80.60  
  Purchase #4 $194.75   8.573%   $211.4459   $211.45   $211.45   $211.40  
  Purchase #5 $60.79   12.168%   $68.1869   $68.19   $68.20   $68.20  
  Purchase #6 $87.57   5.755%   $92.6097   $92.61   $92.60   $92.60  
  Purchase #7 $192.57   12.841%   $217.2979   $217.30   $217.30   $217.30  
  7 purchase totals = $914.24       $994.6117   $994.62   $994.60   $994.60