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 $56.84   10.732%   $62.9401   $62.94   $62.95   $62.90  
  Purchase #2 $189.72   11.144%   $210.8624   $210.86   $210.85   $210.90  
  Purchase #3 $54.56   7.518%   $58.6618   $58.66   $58.65   $58.70  
  Purchase #4 $220.53   7.454%   $236.9683   $236.97   $236.95   $237.00  
  Purchase #5 $104.40   9.691%   $114.5174   $114.52   $114.50   $114.50  
  Purchase #6 $8.59   11.220%   $9.5538   $9.55   $9.55   $9.60  
  Purchase #7 $133.58   10.608%   $147.7502   $147.75   $147.75   $147.80  
  7 purchase totals = $768.22       $841.2540   $841.25   $841.20   $841.40