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 $48.47   10.731%   $53.6713   $53.67   $53.65   $53.70  
  Purchase #2 $106.84   6.615%   $113.9075   $113.91   $113.90   $113.90  
  Purchase #3 $202.72   11.538%   $226.1098   $226.11   $226.10   $226.10  
  Purchase #4 $87.40   5.717%   $92.3967   $92.40   $92.40   $92.40  
  Purchase #5 $158.94   9.797%   $174.5114   $174.51   $174.50   $174.50  
  Purchase #6 $240.94   10.743%   $266.8242   $266.82   $266.80   $266.80  
  Purchase #7 $148.35   5.723%   $156.8401   $156.84   $156.85   $156.80  
  7 purchase totals = $993.66       $1,084.2610   $1,084.26   $1,084.20   $1,084.20