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 $120.64   13.668%   $137.1291   $137.13   $137.15   $137.10  
  Purchase #2 $149.61   8.729%   $162.6695   $162.67   $162.65   $162.70  
  Purchase #3 $206.47   12.346%   $231.9608   $231.96   $231.95   $232.00  
  Purchase #4 $166.29   8.859%   $181.0216   $181.02   $181.00   $181.00  
  Purchase #5 $68.51   12.732%   $77.2327   $77.23   $77.25   $77.20  
  Purchase #6 $249.31   7.707%   $268.5243   $268.52   $268.50   $268.50  
  Purchase #7 $41.26   10.318%   $45.5172   $45.52   $45.50   $45.50  
  7 purchase totals = $1,002.09       $1,104.0552   $1,104.05   $1,104.00   $1,104.00