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 $246.58   7.502%   $265.0784   $265.08   $265.10   $265.10  
  Purchase #2 $92.74   13.147%   $104.9325   $104.93   $104.95   $104.90  
  Purchase #3 $192.75   3.221%   $198.9585   $198.96   $198.95   $199.00  
  Purchase #4 $76.29   12.405%   $85.7538   $85.75   $85.75   $85.80  
  Purchase #5 $141.67   10.336%   $156.313   $156.31   $156.30   $156.30  
  Purchase #6 $220.42   6.782%   $235.3689   $235.37   $235.35   $235.40  
  Purchase #7 $123.42   12.191%   $138.4661   $138.47   $138.45   $138.50  
  7 purchase totals = $1,093.87       $1,184.8712   $1,184.87   $1,184.85   $1,185.00