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 $238.49   10.554%   $263.6602   $263.66   $263.65   $263.70  
  Purchase #2 $55.68   8.249%   $60.273   $60.27   $60.25   $60.30  
  Purchase #3 $190.77   7.148%   $204.4062   $204.41   $204.40   $204.40  
  Purchase #4 $174.32   4.167%   $181.5839   $181.58   $181.60   $181.60  
  Purchase #5 $42.68   6.751%   $45.5613   $45.56   $45.55   $45.60  
  Purchase #6 $131.59   13.812%   $149.7652   $149.77   $149.75   $149.80  
  Purchase #7 $194.33   4.150%   $202.3947   $202.39   $202.40   $202.40  
  7 purchase totals = $1,027.86       $1,107.6445   $1,107.64   $1,107.60   $1,107.80