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 $65.43   3.244%   $67.5525   $67.55   $67.55   $67.60  
  Purchase #2 $152.32   6.779%   $162.6458   $162.65   $162.65   $162.60  
  Purchase #3 $156.52   11.767%   $174.9377   $174.94   $174.95   $174.90  
  Purchase #4 $134.74   3.438%   $139.3724   $139.37   $139.35   $139.40  
  Purchase #5 $96.38   12.293%   $108.228   $108.23   $108.25   $108.20  
  Purchase #6 $199.39   10.673%   $220.6709   $220.67   $220.65   $220.70  
  Purchase #7 $210.37   7.569%   $226.2929   $226.29   $226.30   $226.30  
  7 purchase totals = $1,015.15       $1,099.7002   $1,099.70   $1,099.70   $1,099.70