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 $41.32   6.814%   $44.1355   $44.14   $44.15   $44.10  
  Purchase #2 $128.55   13.441%   $145.8284   $145.83   $145.85   $145.80  
  Purchase #3 $236.79   7.674%   $254.9613   $254.96   $254.95   $255.00  
  Purchase #4 $216.48   6.256%   $230.023   $230.02   $230.00   $230.00  
  Purchase #5 $225.97   13.520%   $256.5211   $256.52   $256.50   $256.50  
  Purchase #6 $60.56   10.764%   $67.0787   $67.08   $67.10   $67.10  
  Purchase #7 $243.74   6.658%   $259.9682   $259.97   $259.95   $260.00  
  7 purchase totals = $1,153.41       $1,258.5162   $1,258.52   $1,258.50   $1,258.50