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 $173.80   13.400%   $197.0892   $197.09   $197.10   $197.10  
  Purchase #2 $243.38   3.647%   $252.2561   $252.26   $252.25   $252.30  
  Purchase #3 $65.90   6.820%   $70.3944   $70.39   $70.40   $70.40  
  Purchase #4 $156.87   8.709%   $170.5318   $170.53   $170.55   $170.50  
  Purchase #5 $181.82   8.668%   $197.5802   $197.58   $197.60   $197.60  
  Purchase #6 $229.35   11.411%   $255.5211   $255.52   $255.50   $255.50  
  Purchase #7 $73.33   3.517%   $75.909   $75.91   $75.90   $75.90  
  7 purchase totals = $1,124.45       $1,219.2818   $1,219.28   $1,219.30   $1,219.30