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 $184.67   6.829%   $197.2811   $197.28   $197.30   $197.30  
  Purchase #2 $131.77   13.841%   $150.0083   $150.01   $150.00   $150.00  
  Purchase #3 $56.80   13.800%   $64.6384   $64.64   $64.65   $64.60  
  Purchase #4 $108.47   13.110%   $122.6904   $122.69   $122.70   $122.70  
  Purchase #5 $202.44   11.186%   $225.0849   $225.08   $225.10   $225.10  
  Purchase #6 $131.44   3.470%   $136.001   $136.00   $136.00   $136.00  
  Purchase #7 $110.99   9.758%   $121.8204   $121.82   $121.80   $121.80  
  7 purchase totals = $926.58       $1,017.5245   $1,017.52   $1,017.55   $1,017.50