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 $62.58   6.311%   $66.5294   $66.53   $66.55   $66.50  
  Purchase #2 $211.33   6.860%   $225.8272   $225.83   $225.85   $225.80  
  Purchase #3 $149.26   9.501%   $163.4412   $163.44   $163.45   $163.40  
  Purchase #4 $121.89   3.545%   $126.211   $126.21   $126.20   $126.20  
  Purchase #5 $212.79   6.454%   $226.5235   $226.52   $226.50   $226.50  
  Purchase #6 $195.51   8.192%   $211.5262   $211.53   $211.55   $211.50  
  Purchase #7 $7.65   4.630%   $8.0042   $8.00   $8.00   $8.00  
  7 purchase totals = $961.01       $1,028.0627   $1,028.06   $1,028.10   $1,027.90