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 $37.88   8.445%   $41.079   $41.08   $41.10   $41.10  
  Purchase #2 $137.49   9.339%   $150.3302   $150.33   $150.35   $150.30  
  Purchase #3 $73.40   3.301%   $75.8229   $75.82   $75.80   $75.80  
  Purchase #4 $85.62   3.338%   $88.478   $88.48   $88.50   $88.50  
  Purchase #5 $164.79   4.655%   $172.461   $172.46   $172.45   $172.50  
  Purchase #6 $82.61   5.731%   $87.3444   $87.34   $87.35   $87.30  
  Purchase #7 $203.46   11.242%   $226.333   $226.33   $226.35   $226.30  
  7 purchase totals = $785.25       $841.8485   $841.84   $841.90   $841.80