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 $56.29   10.315%   $62.0963   $62.10   $62.10   $62.10  
  Purchase #2 $211.50   11.116%   $235.0103   $235.01   $235.00   $235.00  
  Purchase #3 $153.92   9.555%   $168.6271   $168.63   $168.65   $168.60  
  Purchase #4 $6.55   6.822%   $6.9968   $7.00   $7.00   $7.00  
  Purchase #5 $207.31   13.394%   $235.0771   $235.08   $235.10   $235.10  
  Purchase #6 $5.50   5.264%   $5.7895   $5.79   $5.80   $5.80  
  Purchase #7 $243.35   10.255%   $268.3055   $268.31   $268.30   $268.30  
  7 purchase totals = $884.42       $981.9026   $981.92   $981.95   $981.90