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 $81.93   6.472%   $87.2325   $87.23   $87.25   $87.20  
  Purchase #2 $235.31   6.640%   $250.9346   $250.93   $250.95   $250.90  
  Purchase #3 $125.72   8.273%   $136.1208   $136.12   $136.10   $136.10  
  Purchase #4 $234.54   5.439%   $247.2966   $247.30   $247.30   $247.30  
  Purchase #5 $191.33   6.731%   $204.2084   $204.21   $204.20   $204.20  
  Purchase #6 $59.56   6.391%   $63.3665   $63.37   $63.35   $63.40  
  Purchase #7 $120.75   5.573%   $127.4794   $127.48   $127.50   $127.50  
  7 purchase totals = $1,049.14       $1,116.6388   $1,116.64   $1,116.65   $1,116.60