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 $116.58   8.490%   $126.4776   $126.48   $126.50   $126.50  
  Purchase #2 $64.61   13.561%   $73.3718   $73.37   $73.35   $73.40  
  Purchase #3 $224.28   11.647%   $250.4019   $250.40   $250.40   $250.40  
  Purchase #4 $41.39   4.318%   $43.1772   $43.18   $43.20   $43.20  
  Purchase #5 $180.53   13.142%   $204.2553   $204.26   $204.25   $204.30  
  Purchase #6 $190.56   6.572%   $203.0836   $203.08   $203.10   $203.10  
  Purchase #7 $112.33   12.753%   $126.6554   $126.66   $126.65   $126.70  
  7 purchase totals = $930.28       $1,027.4228   $1,027.43   $1,027.45   $1,027.60