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 $84.69   4.139%   $88.1953   $88.20   $88.20   $88.20  
  Purchase #2 $192.29   4.244%   $200.4508   $200.45   $200.45   $200.50  
  Purchase #3 $181.99   8.568%   $197.5829   $197.58   $197.60   $197.60  
  Purchase #4 $173.31   3.467%   $179.3187   $179.32   $179.30   $179.30  
  Purchase #5 $95.70   5.107%   $100.5874   $100.59   $100.60   $100.60  
  Purchase #6 $204.53   12.502%   $230.1003   $230.10   $230.10   $230.10  
  Purchase #7 $155.55   9.452%   $170.2526   $170.25   $170.25   $170.30  
  7 purchase totals = $1,088.06       $1,166.4880   $1,166.49   $1,166.50   $1,166.60