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 $121.57   3.653%   $126.011   $126.01   $126.00   $126.00  
  Purchase #2 $212.77   5.440%   $224.3447   $224.34   $224.35   $224.30  
  Purchase #3 $227.45   8.281%   $246.2851   $246.29   $246.30   $246.30  
  Purchase #4 $204.33   12.837%   $230.5598   $230.56   $230.55   $230.60  
  Purchase #5 $75.81   6.191%   $80.5034   $80.50   $80.50   $80.50  
  Purchase #6 $246.70   11.520%   $275.1198   $275.12   $275.10   $275.10  
  Purchase #7 $136.62   12.149%   $153.218   $153.22   $153.20   $153.20  
  7 purchase totals = $1,225.25       $1,336.0418   $1,336.04   $1,336.00   $1,336.00