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 $97.43   6.850%   $104.104   $104.10   $104.10   $104.10  
  Purchase #2 $148.28   3.135%   $152.9286   $152.93   $152.95   $152.90  
  Purchase #3 $244.52   13.560%   $277.6769   $277.68   $277.70   $277.70  
  Purchase #4 $55.59   11.557%   $62.0145   $62.01   $62.00   $62.00  
  Purchase #5 $133.59   11.153%   $148.4893   $148.49   $148.50   $148.50  
  Purchase #6 $127.80   8.755%   $138.9889   $138.99   $139.00   $139.00  
  Purchase #7 $153.96   4.412%   $160.7527   $160.75   $160.75   $160.80  
  7 purchase totals = $961.17       $1,044.9549   $1,044.95   $1,045.00   $1,045.00