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 $56.97   4.413%   $59.4841   $59.48   $59.50   $59.50  
  Purchase #2 $45.66   4.511%   $47.7197   $47.72   $47.70   $47.70  
  Purchase #3 $153.64   10.239%   $169.3712   $169.37   $169.35   $169.40  
  Purchase #4 $191.65   5.307%   $201.8209   $201.82   $201.80   $201.80  
  Purchase #5 $54.27   11.164%   $60.3287   $60.33   $60.35   $60.30  
  Purchase #6 $200.80   13.569%   $228.0466   $228.05   $228.05   $228.00  
  Purchase #7 $225.85   9.412%   $247.107   $247.11   $247.10   $247.10  
  7 purchase totals = $928.84       $1,013.8782   $1,013.88   $1,013.85   $1,013.80