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 $192.64   4.839%   $201.9618   $201.96   $201.95   $202.00  
  Purchase #2 $170.99   10.797%   $189.4518   $189.45   $189.45   $189.50  
  Purchase #3 $39.29   7.772%   $42.3436   $42.34   $42.35   $42.30  
  Purchase #4 $68.68   8.222%   $74.3269   $74.33   $74.35   $74.30  
  Purchase #5 $239.51   3.582%   $248.0892   $248.09   $248.10   $248.10  
  Purchase #6 $203.84   4.154%   $212.3075   $212.31   $212.30   $212.30  
  Purchase #7 $155.89   5.279%   $164.1194   $164.12   $164.10   $164.10  
  7 purchase totals = $1,070.84       $1,132.6002   $1,132.60   $1,132.60   $1,132.60