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 $213.58   9.824%   $234.5621   $234.56   $234.55   $234.60  
  Purchase #2 $160.77   13.811%   $182.9739   $182.97   $182.95   $183.00  
  Purchase #3 $204.49   13.806%   $232.7219   $232.72   $232.70   $232.70  
  Purchase #4 $43.42   12.640%   $48.9083   $48.91   $48.90   $48.90  
  Purchase #5 $168.85   7.207%   $181.019   $181.02   $181.00   $181.00  
  Purchase #6 $27.56   13.705%   $31.3371   $31.34   $31.35   $31.30  
  Purchase #7 $135.79   6.628%   $144.7902   $144.79   $144.80   $144.80  
  7 purchase totals = $954.46       $1,056.3125   $1,056.31   $1,056.25   $1,056.30