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 $171.41   11.610%   $191.3107   $191.31   $191.30   $191.30  
  Purchase #2 $213.36   10.332%   $235.4044   $235.40   $235.40   $235.40  
  Purchase #3 $5.53   6.693%   $5.9001   $5.90   $5.90   $5.90  
  Purchase #4 $246.75   4.868%   $258.7618   $258.76   $258.75   $258.80  
  Purchase #5 $216.57   13.580%   $245.9802   $245.98   $246.00   $246.00  
  Purchase #6 $62.69   10.811%   $69.4674   $69.47   $69.45   $69.50  
  Purchase #7 $41.81   7.811%   $45.0758   $45.08   $45.10   $45.10  
  7 purchase totals = $958.12       $1,051.9004   $1,051.90   $1,051.90   $1,052.00