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 $201.94   12.563%   $227.3097   $227.31   $227.30   $227.30  
  Purchase #2 $212.81   7.325%   $228.3983   $228.40   $228.40   $228.40  
  Purchase #3 $62.49   4.224%   $65.1296   $65.13   $65.15   $65.10  
  Purchase #4 $76.85   9.704%   $84.3075   $84.31   $84.30   $84.30  
  Purchase #5 $104.65   8.253%   $113.2868   $113.29   $113.30   $113.30  
  Purchase #6 $238.43   7.625%   $256.6103   $256.61   $256.60   $256.60  
  Purchase #7 $30.95   8.529%   $33.5897   $33.59   $33.60   $33.60  
  7 purchase totals = $928.12       $1,008.6319   $1,008.64   $1,008.65   $1,008.60